This application claims the priority benefit of Taiwan application serial no. 89113548, filed Jul. 7, 2000.
1. Field of Invention
The present invention relates to a method of manufacturing a two-color filter.
2. Description of Related Art
In U.S. Pat. No. 5,696,750 titled xe2x80x9cOptical head apparatus for different type of disksxe2x80x9d, Japanese company NEC has proposed an optical head capable of reading different types of optical disks such as CD and DVD. The design employs two light sources of a different wavelength and an object lens. To provide dual focus, various types of holographic optical elements (HOE) design and aperture-limiting elements for adjusting the effective numerical aperture including a combination of the two elements has been proposed in the article.
The aperture-limiting element is a rectangular glass plate having a circular hole in the middle. Diameter of the hole is smaller than the effective diameter of the object lens. A phase compensation layer and an interference filter are sequentially plated over the area outside the hole. Therefore, light beam having a wavelength of 635 nm is permitted to pass through while a light beam having a wavelength of 785 nm is completely reflected back. Meanwhile, the hole permits both 635 nm and 785 nm light to pass through unimpeded. Consequently, when light containing two different wavelengths is beamed onto the aperture-limiting element and focused by the object lens, a pair of focuses capable of reading different types of optical disks is produced.
Although the function and structure of the aperture-limiting element has been disclosed in the aforementioned U.S. Patent, method of manufacturing the aperture-limiting element remains unknown.
Accordingly, one object of the present invention is to provide a method of manufacturing a two-color filter capable of producing a pair of focuses for reading different types of optical disks.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of manufacturing a two-color filter. The method includes the steps: (a) providing a substrate; (b) forming a first metallic layer over the substrate; (c) forming a second metallic layer over the first metallic layer; (d) forming a photoresist layer over a desired region of the second metallic layer; (e) etching to remove a portion of the first metallic layer and the second metallic layer in region not covered by the photoresist layer to form a third metallic layer and a fourth metallic layer over the substrate respectively; (f) forming an optical film over the photoresist layer and the substrate such that the optical film is able to cover only a portion of the sidewalls of the fourth metallic layer or a portion of the third metallic layer through careful adjustment of the thickness of the first and the second metallic layer, or in other words, the third and the fourth metallic layer; and (g) removing the third metallic layer and the fourth metallic layer and at the same time stripping off the photoresist layer so that an optical film previously attached to the sidewalls of the third and fourth metallic layer remains over the substrate.
The invention also provides an alternative method of manufacturing a two-color filter. The alternative method includes the steps: (a) providing a substrate; (b) forming a first metallic layer over the substrate; (c) forming a photoresist layer over a desirable region above the first metallic layer; (d) etching to remove the exposed first metallic layer so that a second metallic layer is formed over the substrate; (e) forming an optical film over the photoresist layer and the substrate such that the optical film is able to cover only a portion of the sidewalls of the second metallic layer through carefully adjusting the thickness of the first metallic layer, or in other words, the second metallic layer; and (f) removing the second metallic layer and stripping off the photoresist layer so that an optical film previously attached to the sidewalls of second metallic layer remains over the substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.